It is.
It is present under the hyperlink on the word "caused" in the Basic Configuration section, where the stock bootloader logic + flag_try_sys2_failed flag are explained with reference to the stock bootloader source code.
Feel free to review: OpenWrt support for Xiaomi AX3000T - #452 by alexq
I would recommend leaving flag_try_sys2_failed= 6 so that the stock bootloader will always attempt to load from firmware 0 (sys1), where you're forcing flag_try_sys1_failed=0 via /etc/rc.local.
But feel free to review the bootloader code yourself and select the best approach.